The disclosures of Japanese Patent Applications Nos. 2001-111544 filed on Apr. 10, 2001 and 2002-7700 filed on Jan. 16, 2002, each including the specification, drawings and abstract, are incorporated herein by reference in their entireties.
1. Field of Invention
The invention relates to an emission control apparatus of an internal combustion engine, and a method for retarding deterioration of an emission control catalyst.
2. Description of Related Art
Among the internal combustion engine emission control apparatuses in which an emission control catalyst is disposed in an engine exhaust passage, there are known internal combustion engine emission control apparatuses that retard the deterioration of an emission control catalyst by preventing excessively high temperatures of the emission control catalyst. An example of this type of internal combustion engine emission control apparatuses is described in Japanese Patent Application Laid-Open No. 9-88563. According to the internal combustion engine emission control apparatus described in Japanese Patent Application Laid-Open No. 9-88563, if the temperature of the emission control catalyst becomes high, relatively low-temperature exhaust gas is supplied to the emission control catalyst, so that the temperature of the emission control catalyst will drop.
The internal combustion engine emission control apparatus described in the patent application reduces the temperature of the emission control catalyst by supplying relatively low-temperature exhaust gas to the emission control catalyst when the temperature of the catalyst is high. However, this laid-open patent application does not disclose at what timing the exhaust gas should be supplied to the emission control catalyst to increase the reducing rate of the temperature of the emission control catalyst. Therefore, the internal combustion engine emission control apparatus described in Japanese Patent Application Laid-Open No. 9-88563 is not able to quickly reduce the temperature of the emission control catalyst. Furthermore, the internal combustion engine emission control apparatus described in this patent application performs reflux of exhaust gas during a high-speed and high-load operation, that is, during an operation region with a high pressure in the exhaust system. Therefore, a pump for supplying exhaust gas needs to have a high capacity.
Japanese Patent Application Laid-Open Nos. 54-55223 and 59-96423 describe internal combustion engine emission control apparatuses in which if the temperature of an emission control catalyst becomes high, the temperature of the catalyst is reduced by supplying secondary air to the catalyst during a decelerating engine operation, to retard the deterioration of the catalyst. In the emission control apparatuses described in these patent applications, a fixed amount of fresh air is supplied to the catalyst regardless of the catalyst temperature. Therefore, there are various problems such as, for example, a failure in sufficiently reducing the catalyst temperature, the excessive cooling of the catalyst caused by the supply of secondary air, degraded fuel economy caused by increased power consumption of a secondary air pump, etc. Further, the internal combustion engine emission control apparatuses supply secondary air to the emission control catalyst regardless of the air-fuel ratio of the atmosphere of the catalyst whenever the temperature of the catalyst is high. Therefore, the supply of secondary air may cause a high catalyst temperature and a lean air-fuel ratio atmosphere. In reality, however, the deterioration of the emission control catalyst is considerably related to the atmospheric air-fuel ratio. For example, if the temperature is high and the atmospheric air-fuel ratio is high (lean), the catalyst particle size tends to increase due to sintering. In general, therefore, the emission control catalyst is most likely to deteriorate in a state of high temperature and lean exhaust air-fuel ratio. However, in the case of the stoichiometric air-fuel ratio or rich air-fuel ratios, the sintering is unlikely to occur and the catalyst undergoes substantially no deterioration even if the catalyst temperature is high.
The invention thus effectively retards deterioration of an emission control catalyst. A first aspect of the invention relates to an emission control apparatus of an internal combustion engine that reduces the temperature of an emission control catalyst disposed in an engine exhaust passage to retard deterioration of the catalyst by supplying fresh air to the emission control catalyst during a decelerating operation of the engine. If a condition for executing a fuel cut operation for stopping the supply of fuel to the engine during the decelerating operation of the engine is met, the internal combustion engine emission control apparatus starts supplying the fresh air to the emission control catalyst before the fuel cut operation starts.
In the emission control apparatus of the internal combustion engine of the first aspect, fresh air is supplied to the emission control catalyst during the decelerating operation of the engine, for example, if the temperature of the emission control catalyst needs to be reduced. Therefore, due to a synergistic effect of the reduction in the temperature of the emission control catalyst caused by the decelerating operation of the engine and the reduction in the temperature of the emission control catalyst caused by the supply of fresh air to the emission control catalyst, it is possible to quickly reduce the temperature of the emission control catalyst. That is, in this aspect, the temperature of the emission control catalyst can be more quickly reduced than in a case where air is not supplied to an emission control catalyst during a decelerating operation of the engine. Furthermore, the emission control apparatus of the first aspect does not require a high durability for a reflux device for refluxing exhaust, such as a pump and the like, and does not need means for cooling exhaust gas. Therefore, cost increases can be avoided.
In some cases, the fuel cut operation of stopping the supply of fuel to the engine is performed during a decelerating operation of the engine. Execution of the fuel cut operation causes an extremely lean air-fuel ratio of engine exhaust gas. During the fuel-cut operation, the exhaust temperature reduces, and therefore the temperature of the emission control catalyst also reduces. At the beginning of the fuel cut, however, the temperature of the emission control catalyst is high. Therefore, a condition of a high temperature and a lean air-fuel ratio is met at the beginning of the fuel cut, and deterioration of the catalyst may be accelerated. In the emission control apparatus of the internal combustion engine of the first aspect, if the fuel cut executing condition is met during a deceleration of the engine, fresh air is supplied to the engine before the fuel cut is actually performed. Therefore, the catalyst temperature starts to drop before the fuel cut is actually started. Hence, acceleration of the deterioration of the emission control catalyst at the beginning of the fuel cut is suppressed.
A second aspect of the invention relates to an emission control apparatus of an internal combustion engine that reduces a temperature of an emission control catalyst disposed in an engine exhaust passage to retard deterioration of the emission control catalyst by supplying fresh air to the emission control catalyst during a decelerating operation of the engine. This emission control apparatus supplies the fresh air to the emission control catalyst when the temperature of the emission control catalyst is higher than a predetermined temperature and an air-fuel ratio is a lean air-fuel ratio.
In the emission control apparatus of the second aspect, only if during the decelerating operation of the engine, the catalyst temperature is high and the air-fuel ratio is on the lean side, that is, only in a case where deterioration of the catalyst will be accelerated, fresh air is supplied to the emission control catalyst to quickly reduce the catalyst temperature. Therefore, the supply of fresh air is performed only when the supply of fresh air is needed in order to retard deterioration of the catalyst. Thus, excessive temperature fall of the catalyst and increase in the engine fuel consumption are suppressed.
A third aspect of the invention relates to an emission control apparatus of an internal combustion engine that reduces a temperature of an emission control catalyst disposed in an engine exhaust passage to retard deterioration of the emission control catalyst by supplying fresh air to the emission control catalyst during a decelerating operation of the engine. The emission control apparatus further has, in an engine intake passage, a throttle valve whose degree of opening is variable independently of an amount of depression of an accelerator pedal. During the decelerating operation of the engine, the emission control apparatus increases the degree of opening of the throttle valve so that an air that has passed through a combustion chamber is supplied as the fresh air to the emission control catalyst.
In the internal combustion engine emission control apparatus of the third aspect, fresh air is supplied to the catalyst via the combustion chamber by increasing the degree of throttle valve opening during the decelerating operation of the engine although the throttle valve is normally completely closed during the decelerating operation. Therefore, it becomes possible to quickly cool the emission control catalyst without using a device for supplying secondary air, such as an air pump or the like.
A fourth aspect of the invention relates to an emission control apparatus of an internal combustion engine that reduces a temperature of an emission control catalyst disposed in an engine exhaust passage to retard deterioration of the emission control catalyst by supplying fresh air to the emission control catalyst during a decelerating operation of the engine. This emission control apparatus sets the amount of fresh air supplied to the catalyst on the basis of the temperature of the emission control catalyst.
In the emission control apparatus of the fourth aspect, the amount of fresh air supplied to the catalyst is set on the basis of the temperature of the emission control catalyst. Therefore, for example, if the temperature of the emission control catalyst is very high, the temperature of the catalyst can be reliably reduced to a temperature range in which deterioration of the catalyst is not caused, by increasing one or both of the amount of flow of fresh air and the duration of supply of fresh air to increase the amount of fresh air supplied to the catalyst. If the temperature of the emission control catalyst is relatively low, the amount of air supplied to the catalyst is reduced, thus suppressing a reduction in the catalyst temperature that is more than necessary.
A fifth aspect of the invention relates to an emission control apparatus of an internal combustion engine that reduces a temperature of an emission control catalyst disposed in an engine exhaust passage to retard deterioration of the emission control catalyst by supplying fresh air to the emission control catalyst during a decelerating operation of the engine. This emission control apparatus supplies fuel to the engine in such a manner that an air-fuel ratio of an exhaust that reaches the emission control catalyst becomes equal to one of a stoichiometric air-fuel ratio and a rich air-fuel ratio when the fresh air is supplied.
This emission control apparatus suppresses the air-fuel ratio of engine exhaust from becoming a lean air-fuel ratio even when fresh air is supplied to the catalyst to reduce the temperature of the catalyst. Therefore, even when the catalyst is in a relatively high-temperature state, such as at the beginning of the supply of fresh air or the like, exposure of the catalyst to lean air-fuel ratio exhaust is suppressed. Thus, accelerated deterioration of the catalyst caused by a high-temperature and lean atmosphere is avoided.
A sixth aspect of the invention relates to a method for retarding deterioration of an emission control catalyst of an internal combustion engine. The catalyst deterioration retarding method of the sixth aspect includes the step of determining whether a condition for executing a fuel cut operation of stopping a supply of fuel to the engine during a decelerating operation of the engine is met, the step of starting supplying fresh air to the emission control catalyst if it is determined that the condition for executing the fuel cut operation is met, and the step of starting the fuel cut operation after the fresh air starts to be supplied.
In the catalyst deterioration retarding method of the sixth aspect, if the fuel cut executing condition is met during a deceleration of the engine, fresh air is supplied to the engine before the fuel cut is actually performed. Therefore, the catalyst temperature starts to drop before the fuel cut is actually started. Hence, acceleration of the deterioration of the emission control catalyst at the beginning of the fuel cut is suppressed.
A seventh aspect of the invention relates to a method for retarding deterioration of an emission control catalyst of an internal combustion engine. The catalyst deterioration retarding method of the seventh aspect includes the step of determining whether the engine is in a decelerating operation, the step of determining a temperature of the emission control catalyst, the step of determining an air-fuel ratio of an exhaust that reaches the emission control catalyst, and the step of supplying fresh air to the emission control catalyst if it determined that the engine is in the decelerating operation, the determined temperature of the emission control catalyst is higher than a predetermined temperature and the air-fuel ratio determined is a lean air-fuel ratio.
In the catalyst deterioration retarding method of the seventh aspect, only if during the decelerating operation of the engine, the catalyst temperature is high and the air-fuel ratio is on the lean side, that is, only in a case where deterioration of the catalyst will be accelerated, fresh air is supplied to the emission control catalyst to quickly reduce the catalyst temperature. Therefore, the supply of fresh air is performed only when the supply of fresh air is needed to retard deterioration of the catalyst. Thus, an excessive temperature fall of the catalyst and increase in the engine fuel consumption are suppressed.
An eighth aspect of the invention relates to a method for retarding deterioration of an emission control catalyst of an internal combustion engine. The catalyst deterioration retarding method of the eighth aspect is intended for an emission control catalyst of an internal combustion engine that has, in an engine intake passage, a throttle valve whose degree of opening is variable independently of an amount of depression of an accelerator pedal. The catalyst deterioration retarding method of whether the eighth aspect includes the step of determining the engine is in a decelerating operation, and the step of supplying air that has passed through a combustion chamber as fresh air to the emission control catalyst by increasing the degree of opening of the throttle valve if it is determined that the engine is in the decelerating operation.
In the catalyst deterioration retarding method of the eighth aspect, fresh air is supplied to the catalyst via the combustion chamber by increasing the degree of throttle valve opening during the decelerating operation of the engine although the throttle valve is normally completely closed during the decelerating operation. Therefore, it becomes possible to quickly cool the emission control catalyst without using a device for supplying secondary air, such as an air pump or the like.
A ninth aspect of the invention relates to a method for retarding deterioration of an emission control catalyst of an internal combustion engine. The catalyst deterioration retarding method of the ninth aspect includes the step of determining whether the engine is in a decelerating operation, the step of determining a temperature of the emission control catalyst, the step of setting an amount of fresh air on the basis of the determined temperature of the emission control catalyst, and the step of supplying the emission control catalyst with the set amount of fresh air if it is that the engine is in the decelerating operation.
In the catalyst deterioration retarding method of the ninth aspect, the amount of fresh air supplied to the catalyst is set on the basis of the temperature of the emission control catalyst. Therefore, for example, if the temperature of the emission control catalyst is very high, the temperature of the catalyst can be reliably reduced to a temperature range in which deterioration of the catalyst is not caused, by increasing one or both of the amount of flow of fresh air and the duration of supply of fresh air to increase the amount of fresh air supplied to the catalyst. If the temperature of the emission control catalyst is relatively low, the amount of air supplied to the catalyst is reduced, thus suppressing a reduction in the catalyst temperature that is more than necessary.
A tenth aspect of the invention relates to a method for retarding deterioration of an emission control catalyst of an internal combustion engine. The catalyst deterioration retarding method of the tenth aspect includes the step of determining whether the engine is in a decelerating operation, the step of setting an amount of fuel injected so as to make an air-fuel ratio of an exhaust that reaches the emission control catalyst equal to one of a stoichiometric air-fuel ratio and a rich air-fuel ratio, and the step of supplying the set amount of fuel to the engine if it is determined that the engine is in a decelerating operation.
The catalyst deterioration retarding method of the tenth aspect suppress the air-fuel ratio of engine exhaust from becoming a lean air-fuel ratio even when fresh air is supplied to the catalyst to reduce the temperature of the catalyst. Therefore, even when the catalyst is in a relatively high-temperature state, such as at the beginning of the supply of fresh air or the like, exposure of the catalyst to lean air-fuel ratio exhaust is suppressed. Thus, accelerated deterioration of the catalyst caused by a high-temperature and lean atmosphere is avoided.